Sorry for the trouble this is causing! From the error message, it looks like we were successful in uploading the new version of the document up to the server with a temporary name, but when we tried to remove the old one and rename the new copy, there was a problem. If you email the
support ninjas, we can look into this with you.
In the meantime, you can use the "Go" menu on your Mac to connect to the Omni Sync Server and delete the extra file from your account. Just enter "https://sync.omnigroup.com/<your account name>" into the "Server Address:" field, then press the Connect button and enter your username/password when they're requested.